'It's a ridiculous building, isn't it?" says Chris Addison. We're hurrying past the Houses of Parliament. "It needn't have looked like something built by and for a toddler. But it does. It looks like a play castle for a three-year-old."

We're trying to get inside this play castle to hear shadow business secretary Kenneth Clarke's speech to the press gallery's lunch club. The idea is to give Addison, who plays the baby-faced political adviser Ollie Reeder in The Thick of It, the inside track on a Tory bigwig who will – perhaps – be a leading minister in the next administration and thus a future butt of the comedy's satire. After all, Clarke is a close approximation of the show's suave, world-weary shadow minister Peter Mannion, if not quite as lecherous.

As we walk, Addison receives some furtive don't-I-know-you-from-telly glances. Quite possibly some are wondering about the truth of spin doctor Malcolm Tucker's description of Reeder as an "unbaked gingerbread man". "I only get recognised within a quarter-mile radius of Millbank," Addison says. With loathing or fondness? "Not loathing. The people who work in the Westminster political village love The Thick of It."

Even though the sitcom portrays them as venal, spineless, foul-mouthed buffoons? "People don't think it's about them personally. Roy Clarke, who wrote Keeping Up Appearances, said that women in floral-print dresses were always coming up to him saying, 'I love that show. I know so many women who are like Hyacinth Bucket.' It's the same with The Thick of It. They don't think it is about them, but it is."

Its critics say The Thick of It is too cynical about politics. Addison disagrees. "The people who are cynical about politics are newspapers, not us. Look at that," he says, pointing to a billboard for the London Evening Standard that reads: "Tape exposes Brown." "That's a political move by the rightwing press," he says. "We've not done anything like that. I mean, the prime minister handwrote a note and they do him. I'm not a big fan of Brown, but going after him like that is really cynical." It's a good point, made, ironically enough, by a standup comic and actor who is currently an Evening Standard columnist. "Not for much longer, though – they're getting rid of me."

Addison argues that The Thick of It has morals. "Malcolm Tucker [the government's communications director, played by Peter Capaldi] is a monster, but he's doing it for a purpose – not for the purpose of being unpleasant but to keep his party in power. Nicola Murray [the new social affairs and citizenship secretary] really wants to do good. They're stopped from succeeding by the everyday, as are most people when they try to do anything. It's about how people react under pressure. Just because these people appear to be acting on a bigger scale ups the jeopardy of it."

Is Murray based on Harriet Harman or Jacqui Smith? "Neither – she's a composite. Rebecca [Front, who plays Murray] spoke to a former Cabinet member, but nobody's guessed which, and they won't." Interesting. Which ex-Cabinet minister could it have been? Hazel Blears (who, like Murray, desperately wants to be seen as fun, not po-faced) fits the bill. As does Jacqui Smith. I see a lot of Tessa Jowell in Murray's I'm-poised-to-lose-it-here-big-style vibe, and not a lot of Harriet Harman. Addison won't be drawn: "It's really an astonishing performance by Rebecca, of her own personality, which is how it has to be because so much of it is improvised."

So, following that logic, does Ollie Reeder – arrogant, bumbling, fast-tracked Oxbridge twerp – have something of Chris Addison in him? "How dare you!" he laughs. "I did English at Birmingham, I'll have you know." We go through the Westminster security check. Once inside, Addison wipes his brow. He's never been here before. "How can you think clearly – to legislate for the benefit of the country – when it's so hot? All these corridors and little rooms! It's clearly designed for intrigue." We hurry to catch Clarke's speech. "Wonder what it'll be about?" asks Addison. "Jazz, hopefully."

Clarke, rubicund and roly-poly, is winding up, predicting the Conservatives will "probably win", before facing questions. "This is a man I regarded with total hatred when I was a student and he was education secretary," hisses Addison. "I remember going on a demo with 50,000 students protesting about housing benefit and I saw him on the news saying, 'Students had a party in London.'"

Despite this, he admits to a performer's admiration for the way Clarke works the room. Could Ollie Reeder work with Ken Clarke? "Clarke would be funnier than anybody else in the room. That would be dreadful for Ollie. He needs to be the funniest person in the room."

Will The Thick of It continue into the next decade, and satirise what may be a new political culture? After all, Armando Iannucci's creation was surely inspired by Alastair Campbell's diaries and has New Labour's spin-doctoring at its heart. "It's ended up being a long way from that," says Addison. "But I really want it to carry on, and I want there to be a sequel to In the Loop [the film based on The Thick of It]. But that's all down to Armando."

New role as a headmaster

One thing is certain about Addison's TV career: his 2008 BBC2 sitcom Lab Rats won't get a second series. Why not? "No future for multi-camera sitcoms like that – they cost too much." That's one reason. Another is that critics, while liking Addison's writing, thought the sitcom, about university scientists getting into a weekly scrape, was at least two decades out of date; the characters were as stereotypical as Are You Being Served's. To my mind, though, that was its charm.

Instead, he has just recorded a small part in Skins, E4's youth drama, in which he plays a headmaster who is a "Cameronian control freak – an uptight, smug bully who, it seems to me, is less interested in teaching than in 'fixing' youth". He admits that playing the role makes him feel incredibly old. "That said, I think Skins makes anyone above the age of 23 feel old, and that's one of its great strengths. It's energetic, colourful and full of life in a way that not much drama is on TV these days, so it's a combination of fun and terrifying to watch if you're out of its immediate demographic – particularly terrifying if you're a parent of teenagers, I should think. You are always aware when watching it that it's Not Meant For You."

Addison, who regards himself as a standup who strayed into acting, is also honing his comedy routine ahead of a national tour."The mind of the standup works like this," he says. "If there's one person in the room who's not laughing, that's all I focus on." Now 38 and married with two kids, Addison started as a standup in Manchester in the mid-90s. "I wanted to be a theatre director but I'm too lazy, and standup is very simple." How did you get into it? "There's that year when you've left university which is a chasm. It's profoundly depressing when you realise what you can't do. I can't draw, I can't play music, but I can show off. People suggested standup – you just turn up and say some words. That's what I do."

He learned his trade in Manchester. "It was a big time for comedy in Manchester. Steve [Coogan], Caroline Aherne, Johnny Vegas, Peter Kay were all around. There's a fundamental lesson I learned early on. I took a lit cigarette on stage with me – I assumed, being a fresh-faced middle-class young man in a north Manchester pub, that a cigarette would give me some credibility. That was probably undermined by wearing a waistcoat. I bombed."

Next time, Addison, the son of a teacher mum and doctor dad, played up his middle-class persona. "I went on as Posh Boy and did stuff about burgling Moss Side while the people who lived there were off seeing Oasis gigs. It worked. There were lots of pretend geezers on the comedy circuit, blokey blokes. So when I went on doing observations about hummus, it was unusual."

When comedy goes too far

He recently caused offence at a corporate gig for hedge-fund traders. "It was about the proposal that they should have to go on a register. I suggested that would be good for paedophiles because they would ­ become the second most despised group of people who have to put their name on a list." Hilarious. "Not really. Generally, people like being mildly ribbed. The people who don't are people who have to make a terrific effort to believe what they're doing is worth getting out of bed for."

The question of offensiveness bothers Addison. What did he feel about Jimmy Carr's joke ("Say what you like about those servicemen amputees from Iraq and Afghanistan, but we're going to have a fucking good Paralympic team in 2012")? "I stand by whatever the majority of soldiers think about it. The majority of soldiers – not their families. The thing that got lost in the row was that the Paralympics were started for people who were wounded. It would be interesting to see if they're offended."

Another worry is having his material blabbed all over the internet halfway through a tour, thus making it unusable. "When Dan Antopolski won the best joke at Edinburgh this year, it was repeated all over the internet. I texted him, 'That's your joke fucked.' And it was." So tell me some of the gags from your new show so I can blab them. "I think not. I haven't written it yet and I'm terrified." So you're a neurotic? "I'm getting worse as I get older. I suffer the same panics everybody does – about getting found out. Everybody thinks, 'Jesus, when will they take me away in a silver blanket, give me a mug of cocoa and everything will be all right?' I'm no different."